LibWeb: Paint inspection outline for InlineNodes :^)

This iterates the fragments of the containing block, and paints their
outlines if they are descendants of the InlineNode.

If multiple fragments are adjacent, eg:

```html
<span><b>Well</b> hello <i>friends!</i></span>
```

...then we get a double-thick outline between "Well", " hello " and
"friends!", but we can come back to this after we implement
non-rectangular outlines for the `outline` CSS property.

Userland/Libraries/LibWeb/Layout/InlineNode.h

@@ -15,6 +15,7 @@ public:
     InlineNode(DOM::Document&, DOM::Element&, NonnullRefPtr<CSS::StyleProperties>);
     virtual ~InlineNode() override;
 
+    virtual void paint(PaintContext&, PaintPhase) override;
     virtual void paint_fragment(PaintContext&, const LineBoxFragment&, PaintPhase) const override;
 
     virtual void split_into_lines(InlineFormattingContext&, LayoutMode) override;